1. Field of the Invention
The present invention relates to an apparatus for optically transmitting serial data in a multiplex mode through an optical transmission path such as optical fiber, optical waveguide and free space by utilizing a hole-burning effect.
2. Related Art Statement
In a known optical communication system, an amplitude of light, i.e. an intensity of light is modulated in accordance with data to be transmitted and the light having the thus modulated intensity is transmitted through an optical transmission path. In this case, in the optical transmission path such as an optical fiber, binary signals are serially transmitted in a time domain. Since a laser diode serving as a transmission light source has a superior modulation property, the laser light has a very high vibrating frequency and the transmission path has a low dispersion, it is possible to attain a high transmission speed up to several giga bits per second.
Nowadays an amount of data to be transmitted has been increased largely and it has been desired to increase the data transmission capacity by affecting the multiplex data transmission without increasing the number of optical fibers. As the optical multiplex data transmission system, a wavelength multiplex data transmission system has been proposed. In this known wavelength multiplex data transmission system, the transmission data is multiplexed in a frequency domain. That is to say, there are provided a plurality of laser light sources which emit laser light beams having different wavelengths and an intensity of each of these laser light beams is modulated by a respective one of a plurality of transmission data signals. These modulated light beams are simultaneously transmitted through one and the same optical fiber. Usually, two to four wavelengths are selected from 0.81 .mu.m, 0.85 .mu.m, 0.89 .mu.m, 1.2 .mu.m, 1.3 .mu.m and 1.55 .mu.m.
In such a known wavelength multiplex transmission system, a multiplexing factor amounts to at most 5, so that a multiplex transmission efficiency is low. For instance, in case of applying the transmission system to the computer data processing, it is desired to transmit at once information data of one byte (8 bits) or more. Moreover, the processing speed and data transmission capacity of the computer system have become increased, so that it is required to develop a novel transmission system in which several tens to one hundred channel data can be transmitted simultaneously. Such a requirement will meet a data transmission in a future high speed parallel processing computer.
In a field of a data communication system which links computers with each other, in case of performing data links between computers and between a computer and a plurality of terminal devices, it is necessary to utilize a single transmission path at a high transmission efficiency. In order not to decrease the data transmission speed, there has been proposed a packet transmission system using the time division method. In the known packet transmission system, an electrically operating multiplexer-demultiplexer is used, so that if the packet transmission system is applied to the optical data transmission system, it will be necessary to convert the light signal into an electrical signal. Then, the whole system is liable to be complicated in construction and expensive in cost.